The present invention relates generally to compositions of matter, apparatuses and methods useful in detecting, identifying, and measuring the precise amount of Hydrogen Fluoride (HF) in a sample of Oxide Etchant used in the manufacture of micro-electronic components.
As described for example is U.S. Pat. Nos. 7,928,368, 6,849,463, and 8,222,079, in the manufacture of micro-electronic components it is quite common to etch the wafer substrate of those components. Etching is the process of removing silicon containing substrate material from the wafer, especially from its surface. Etching commonly involves removing discrete amounts of silicon (or other) material from the wafer to expose other materials layered in the wafer such as buffers, masks, and/or insulation. Etching is also performed to clean the wafer surface, to polish the wafer surface to a desired degree of smoothness, and/or to create reservoirs or channels in the substrate for thermal or electrical shielding purposes or into which devices or other materials can be placed. Etching is a very precise process and it only removes the specific targeted material and/or desired shape in the substrate. In fact Etching can be fully isotropic but sometimes is also anisotropic.
Etching is often performed by a number of processes including the use of high temperature plasma and chemicals such as buffered oxide etchants (BOE). A commonly used buffered oxide is a composition comprising HF such as HF—HNO3 mixtures and/or HF—NH4F mixtures. These HF bearing mixtures are used because it is highly isotropic for silicon, the most common material used in wafer substrates. Unfortunately using HF involves very low tolerances for dosage errors. This is because the magnitude of the amount of silicon etched away by an HF application alters dramatically with even slight changes in the concentration of HF in a given applied dosage. This intolerance is compounded by the fact that the wafer material and targeted etches are micro-scale in size so even slight alterations in silicon removal amounts can utterly ruin the would-be micro-electronic component. As a result, it is extremely important to have highly accurate measurements of the actual amounts of HF species present in the etching composition being used.
In addition, as described in the scientific paper Chemical Analysis of Acidic Silicon Etch Solutions II. Determination of HNO3, HF, and H2SiF6 by on Chromatography, by Jörg Acker, Talanta Volume 72, pp. 1540-1545 (2007), HF and nitrogen bearing species in the composition undergo highly complex equilibrium mechanisms and are also highly toxic and difficult to handle. This makes it impractical and non-economic to use common industry analytical methods for reliably measuring HF levels in a sample.
In addition the intolerance, toxicity, and reactivity make common inventorying procedures impossible with HF etching compositions. Commercially prepared HF etching compositions come in a variety of dosages and concentrations. In normal manufacturing processes, the particular compositions purchased would be the optimal application of available supply and demand. The purchased compositions are then diluted and mixed using standard stoichiometric techniques to obtain a desired dosage concentration. This process however can't be done with HF containing BOE compositions because mixing two or more non-identical compositions results in losing knowledge regarding the exact concentration of HF (or at best it can only be done with cumbersome recordkeeping). Because of the low tolerances inherent in HF use, this results in industry avoiding mixing differently concentrated samples of HF and therefore incurring unwanted costs and inefficiencies.
Thus it is clear that there is definite utility in novel methods and compositions for the proper detection, identification, and measurement of HF in buffered oxide etching compositions. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “Prior Art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.